A lighting device that uses a laser as a light source is disclosed in Patent Document 1 (Japanese Unexamined Patent Application Publication No. 2012-088451). This lighting device was realized with a view to resolving the problem of how to effectively reduce uneven luminance of illumination light while achieving miniaturization and improving the utilization efficiency of light and is provided with: a light source unit that has a plurality of types of laser elements that emit light of different wavelengths; a parallelizing optical system that emits each incident light beam from the plurality of types of laser elements as separate parallel light beams; an optical path synthesizing optical system that carries out optical path synthesis for each parallel light beam that is emitted from the parallelizing optical system; a magnifying optical system that magnifies the beam diameter of each parallel light beam that follows optical path synthesis and emits the resulting light beam; and a uniformizing optical system that uniformizes the in-plane intensity distribution of each parallel light beam that is emitted from the magnifying optical system.
The above-described lighting device is used in a display apparatus such as a projector that displays images. One form of projector performs 3D display. In addition to the typical constituent elements of a projector such as a light source, an image-forming unit that uses the light from the light source to form image light, and a projection optical system that projects the image light that was formed in the image-forming unit, a projector that performs 3D display is further provided with a modulator that modulates the image light that is to be projected to right-eye display image light and left-eye display image light.
The image-forming unit generates an image by switching the right-eye image light and left-eye image light in a time series. The modulator is a component that is configured to enable control of the orientation of the linearly polarized light that is transmitted, and when transmitting right-eye image light and left-eye image light, transmits linearly polarized light having a mutually different orientation, whereby the right-eye projected image light and left-eye projected image light that are the mutually different linearly polarized light are projected in order.
Laser diodes are used as a plurality of laser elements to form the laser light source, and when used in a projector device that performs 3D display as described above, the fact that the laser light is linearly polarized light results in a potential that, when the light is projected through a modulator and projected at the time of 3D display, color uniformity and luminance uniformity will be degraded, leading to the occurrence of uneven color and uneven luminance on the screen. The operation of the modulator that switches the linearly polarized light that is transmitted is next described with reference to drawings.
As shown in FIG. 1, when absorption axis 1b of modulator 1a and the orientation of linearly polarized light 1c that is irradiated into modulator 1a differ by 90 degrees, linearly polarized light 1c is transmitted through modulator 1a. 
As shown in FIG. 2, when absorption axis 1b of modulator 1a and the orientation of linearly polarized light 2c that is irradiated into modulator 1a are the same, linearly polarized light 2c is not transmitted through modulator 1a. 
As shown in FIG. 3, when absorption axis 1b of modulator 1a and the orientation of linearly polarized light 3c that is irradiated into modulator 1a differ by 45 degrees, linearly polarized light 3c is attenuated and transmitted.
When linearly polarized light is transmitted through glass such as a lens that makes up the projection optical system of a projector, disruption of the orientation of the linearly polarized light may occur. This disruption differs according to the point of transmission through the lens (glass), and consequently, the use of a plurality of laser diodes results in the occurrence of a nonuniform state of disruption that differs for each of the laser diodes. As a result, uneven color and uneven luminance occur in the image that is projected through the modulator.
As shown in FIG. 4, when the plurality of laser diodes are arranged such that the orientation of linearly polarized light that is emitted is the same, the orientation of the linear polarized light of the synthesized light of the light from each of the laser diodes is uniform. Subsequent transmission through glass causes the orientation of the linear direction to vary according to the site of the image, as shown in FIG. 5.
When light of the state shown in FIG. 5 passes through a modulator, the quantity of light that is transmitted changes according to the site of the image and uneven color and uneven luminance occur. FIG. 6 shows an example of uneven luminance. Even in a case of using an image signal for display of a screen having uniform luminance, the luminance of site Ea on the projection screen is higher than the luminance of site Eb and uneven luminance occurs.
The symptom of uneven color is described taking as an example a projector that uses as light sources blue laser light as a blue light source and red and green light that are obtained by irradiating the blue laser light as an excitation light upon a fluorescent material that emits yellow fluorescent light and then separating the yellow fluorescent light that is generated.
The yellow fluorescent light and the red and green light that are obtained from this light are not linearly polarized light, and only the blue light that is laser light is linearly polarized light.
When a plurality of laser diodes that emit blue laser light are arranged such that the orientation of the linearly polarized light that is emitted is the same as shown in FIG. 4 and then caused to pass through a modulator, the luminance of site Ea is higher than the luminance of site Eb for the blue light, as shown in FIG. 6. On the other hand, the red light and green light are not linearly polarized light, and the luminance is therefore uniform within the screen. As a result, even when using a picture signal that displays a picture of uniform color on the entire screen, the color of site Ea will differ from that of site Eb, and uneven color will occur.
When carrying out 3D display, when the modulator transmits right-eye image light and left-eye image light, the orientation of the linearly polarized light that is transmitted is assumed to differ, and when a plurality of laser diodes are used as the light source and the orientation of the linearly polarized light of each laser diode is made uniform, the above-described uneven luminance or uneven color will occur.
Patent Document 2 (Japanese Unexamined Patent Application Publication No. H07-22706) discloses a configuration in which the polarization direction of half of the plurality of laser diodes is made different from the polarization direction of the other half. Cited document 2 describes the ability to readily provide stereoscopic display through the use of polarizing means, i.e., polarizing glasses in which, for example, polarizing plates that transmit light that is parallel to each of the polarized waves are arranged on the right and left, and in the case of such a construction, the polarizing means acts as a modulator and therefore results in the occurrence of uneven luminance or uneven color.